Stable reduction products of dyestuffs of the indigo series, and a process of producing same



Patented June 23, 1936 UNITED STATES STABLE REDUCTION P tODUo'rsoF DYE- STUFFS OF THE INDIGO SERIES, AND A PROCESS OF PRODUCING SAME Eduard Muench and Robert Wiminer; Ludwigshafen-on-the-Rhine, Germanyi as'signors to General Aniline Works, Inc., New York, N. Y., a corporation of Delaware No Drawing; Application September 10, 1932 Serial No. 632,634. In Germany September 18,

The present invention relates to new stable re"- duction products of dyestuffs of the indigo series and a process of producing same.

It has already been proposed to reduce indigo and similar coloring matters such as tolylindigo, bromindigo and thioindigo by means of zinc dust and sulphurous acid or a bisulphite or a hydrosulphite' with or without the addition of sulphurous acid in the presence of alcohol in such a quantity and of such a concentration that the indigo-white remains in solution while the salts formed during the reduction remain practically undissolved. When working according to the said process reduction products are obtained which are practically completely soluble in cold aqueous solutions of caustic alkalies.

We have now found that new stable reduction products of halogenated dyestuffsof the indigo series are obtained by heating the leuco com pounds of the said dyestuffs, preferably in the presence of weakly acid agents and'of solvents suchas alcohol and. dlluents such as water'until compounds'are formed which are dimcultly solume or insolublecold solutions of caustic alkalies.-

The process according. to the present 'invention may be carriedout by reducing the dyestuffs or their dehydro compounds in the usual manner in alkaline, neutral oracid media, the free leuco compounds being heatedsimultaneously or directly subsequently or after isolation either alone or with acid agents, as for exampledilute acids, or acid salts, until the new compounds are formedwhich, contrasted with'the leuco compounds proper, are difiicultly soluble or insoluble in cold dilute aqueous solutions of caustic. alkalies, as for example 5 per. cent solutions. of caustic soda or potash. The: reduction of" the dyestuffs to the leuco compounds may be carried out catalytically withhydrogen or by means of alkali metal hydrosulphites or ammonium formate and sulphur dioxide or zinc and aceticacld'. The compounds which are diflicultly soluble or insoluble in. cold aqueous solutions of alkalies may be obtained directly in one working operation by efiecting the reduction in the absence oil. alkalies or alkaline earths or with an addition of smaller amounts of these than are necessary for the formation of the monometallic salts of the leuco compounds and heating hereby until the conversion is complete. It will. be understood that in. this case during the formation. of the leucov compounds the saidsmall. amounts. of solutions of. alkalies or alkalineearths which may be presentare used up so. that the iormation 8 Claims. (Cl. 2 0-521 of the new stable reduction products is not unfavorably influenced thereby. In this case the said alkaline solutions act as a solvent for the leuco compound.

If the preceding formation of the leuco compounds by' reduction of the dyestulis has been carried out in an alkaline medium, the solution of the leuco compound is acidified with acids, such as sulphur dioxide, hydrochloric acid, oxalic acid and tartaric acid or acid salts, such as sodium bisulphite, sodium bisulphate and potassium bitartrate and the mixture is then heated, preferably while adding solvents, such as alcohols, dioxane and glycol ethers until the conversion into the products which are insoluble or diificultly soluble in cold aqueous alkali solutions is completed. It is preferable to employ such amounts of solvents as are not'sufiicient for dissolving completely the-reduction products formed. It will be understood that the process is not carried out in a very strongly acid solution as thereby at least a partial decomposition would be caused. The conversion of the leuco compounds into the new stable reduction productsisjeffected at temperatures above 50 0., generally below CL, preferably the reaction mixture is heatedto the boiling point. The reduction may be carried out under ordinary or under increased pressure.

When the reduction is effected by means of hydrogen in the presence of catalysts it is advantageous to work underincreased pressure. When employing other reducing agents, the reaction is generally carried out under atmospheric pressure. p In many cases it is preferable to 'carry out the reduction of the halogenated dyestuffs of the indigo series and the treatment of their leuco compounds with acid agentsin one operation, if necessary with simultaneous or subsequent evaporation or while distilling off the solvent or diluent- The liquid may either be distilled oif entirely or only until the reduction products separate. 7

The new reductionproducts are generally speaking colorless or only slightly yellow or greenish. They differ from the corresponding leucocompounds mainly by the fact that they are stable in the air, i. e. they do not change into the corresponding dyestuffs when exposed to the atmosphericv ,air. They may therefore be dried without any special precautions. They solve readily in hot aqueous alkalies andin cold alcoholic alkali solutions and form thereby the salts of true leuco compounds. When worked up dis-.

converted into the leuco compounds by steaming.

The new compounds have the great technical advantage that they may be employed for dyeing and printing without the necessity for reducing agents, such as hydrosulphites or formaldehyde sulphoxylates. The stability of the new reduction products also renders it possible tobring the halogenated indigo dyestuffs into commerce in a high-percentage form, because no ditions are necessary.

The following examples will further illustrate the nature of this invention but the invention is not restricted to these examples. The parts ar by weight.

Example 1 A mixture of 200 parts of a 20 per cent paste of 5,5,'l,'l'-tetrachlorindigo-, 50 parts of a per cent solution of ammonium formate and 400 parts of alcohol is heated to boiling under a reflux con-' denser while stirring well, 12 parts of sulphur dioxide are introduced in a slow stream into the boiling mixture. The originally dark blue reaction mass gradually assumes a green color which changes to yellow after about Ahour. The whole is boiled for another hour, whereby the greater part of the new reduction product separates, and the alcohol is then distilled off as completely as possible at atmospheric pressure. The resulting, almost colorless reduction product is then washed with water to free it from salts. The new reduction product of tetrachlorindigo is insoluble in cold water containing alkali and may be .;dried to a completely stable product even-without excluding air. By boiling it with alkali solutions or by treatment with alcoholic alkali solutions in the cold it is converted into the form of the true leuco compound in solution.

Ewample z I y 7 200 parts of a 20 per cent paste of 5,5,'7,7-

:tetrabromindigo are heated to 60 C. with '75 parts of water and 400 parts of alcohol and, then, 30

' parts of anhydrous sodium hydrosulphite are added. While stirring well, the reaction mass is heated to boiling under a reflux condenser, whereby the dyestufi goes completely .intosolution as the leuco compound with a deep yellow coloration. After boiling for half anhour, a separation commences, and this continually increases with further boiling. After boiling for 2 hours the alcohol is distilled off as in Example. 1 and the resulting reduction product is worked up in the same manner as in Example 1. The almost colorless product obtained is insoluble in cold alkaline water, is entirely stable in a dry form and is eminently suitable for the preparation of prints without the addition of a reducing agent being necessary.

Example3 v 10,000 parts of a 20 per cent paste of a 517,537,- tetrabromindigo, obtained by the bromination of indigo in sulphuric acid, are mixed in a stirring pressure-tight vessel with 120 parts of a nickel catalyst (containing 25 per cent of reduced nickel on kieselguhr as a carrier) which is suspended in 1500 parts of water and with a solution of 27 parts of sodium hydroxide in 700 parts of water. Hydrogen is then pressed in and, at an initial pressure of from 8 to 10 atmospheres and at about C., the mixtureis stirred until no further absorption of hydrogen takes place. This is the case after about 5 hours. The wholeis then stirred for 3 hours at a pressure of 6 atmospheres. A practically white suspension of the preserving adtai' ned in a very good yield.

' new reduction product of the 5,7,5,7-tetrabromindigo is formed. This product is filtered off and washed with water, small amounts of the sodium salt of the leuco compound of the tetrabromindigobeing present in the filtrate. The new product does not dissolve in cold dilute aqueous caustic soda solution but dissolves in boiling dilute caustic soda solution giving a brownish yellow, coloration. By blowing this solution with air, the 5,7,5',7-tetrabromindigo may be practically completely recovered.

Example 4 parts of a 40 per cent paste of 5,5-dibromindigo are made into a paste with 1500 parts of water and heated to 60 C. After adding 30 parts of anhydrous sodium hydrosulphite and 25 parts of 34 per cent caustic soda. solution the dyestufi' is completely reduced and precipitated as the free leuco compound by leading sulphur dioxide into the mixture. After filtering bysuction and washing with watera paste is obtained which passes completely'into solution in the cold with dilute alkali solutions.- The-paste is then made into a paste with 400 parts of alcohol while excluding air and is heated to boiling for 2 hours under a reflux condenser after the addition of .100 parts of 38 per cent sodiiun'bisulphite solu- .10 partscf tribromindigo red are made into a paste with .100. parts of alcohol and 40 parts of water, 25 parts of a 45, per cent solution of ammoniumformate then being added. ,At the boiling point of the alcohol, 5 parts of, sulphur dioxide are led in and boiling is continued for 2 hours under a reflux condenser. 1After distilling off the alcohol, a reduction product of tribromindigo red is obtained which has the same properties as regards solubilityiinalkalies'and stability as the products obtained according to the foregoing examples.-

Example 6 200 parts of an aqueous paste of 5,7 ,5,7 '-tetrabromdehydroindigo acetate, corresponding to a content of 4 6 parts of tetrabromindigo, are made into a paste with .100 parts of 38 per cent bisulphite soluti0n, 75 parts" of a 45 per cent ammonium formate solution and 400 parts of alcohol vchange?after boiling for another 2 hours into a practically colorless pulp. The alcohol is distilled off at atmospheric pressure, the reaction mixture is diluted with water and the new reduction product is filteredofi by suction and washed. After drying at waterbath temperature in the air, the product which is described in Example 2 is ob- Ezcample 7 "parts 'of anhydrous'sodiuzn hydrosulphite are added at this temperature. Then the reacting mixture is heated to boiling under a reflux condenser. 'I'hereupon the alcohol is distilled off completely and the reaction mixture is diluted with water. The stable leuco compound precipitated thereby is filtered off by suction, washed and dried in the vacuo at 80 C.

Example 8 50 parts of 4,4-dichlor-5,5'-dibromindigo are mixed with 270 parts of alcohol, 200 parts of water and 40 parts of a per cent aqueous ammonium formate solution. This mixture is heated to boiling under a reflux condenser and 15 parts of sulphurous acid are introduced in a slow stream into the boiling liquid. After heating for 5 hours the alcohol is distilled oil. The stable almost colorless leuco compound thus obtained which is insoluble in cold aqueous solutions of caustic alkalies is isolated as described in Example '7.

Example 9 200 parts of 4,4'-dichlorindigo, 1450 parts of alcohol and 820 parts of water are reduced with 150 parts of anhydrous sodium hydrosulphite in the manner described in Example 7 whereby a greenish-gray leuco compound stable to dilute caustic alkali solutions is obtained.

What we claim is:

1. Reduction products of halogenated dyestuffs of indigo and its derivatives which are practically insoluble in cold aqueous solutions of caustic alkalies, which are colorless to slightly yellow or greenish and which are stable in the air.

2. An almost colorless reduction product of 5,5',7,'7-tetrachlorindigo which is practically insoluble in cold aqueous solutions of caustic alkalies, and stable in the air.

3. An almost colorless reduction product of 5,5',7,'7'-tetrabromindigo which is practically insoluble in cold aqueous solutions of caustic alka- 5 lies, and stable in the air.

4. An almost colorless reduction product of a 5,5'-dibromindigo which is practically insoluble in cold aqueous solutions of caustic alkalies, and stable in the air. 10

5. An almost colorless reduction product of 4,4-dichlor-5,5-dibromindigo which is practically insoluble in cold aqueous solutions of caustic alkalies, and stable in the air.

6. The process of producing a stable reduction 15 product of a halogenated dyestufi of the indigo series which comprises heating the free leuco compound of the said dyestufi with a weakly acid agent at a temperature between 50 and in the presence of a solvent and of a diluent, until 20 the reaction product is practically insoluble in a cold aqueous solution of a caustic alkali.

'7. A stable reduction product of a tetrahalogeno-indole indigo dye, said reduction product being stable to air, insoluble in water, and yielding 25 prints in the usual manner but with smaller amounts of reducing agent than required in the case of the dyestuff proper.

8. A stable reduction product of 4,4-dichloro- 5,5dibromo-indigo, said reduction product being 39 stable to air, insoluble in water, and yielding prints in the usual manner but with smaller amounts of reducing agent than required in the case of the dyestuff proper. v

EDUARD MUENCH. ROBERT WIMMER. 

